Buzz
Caramelizing onions always takes longer than expected. A lot of the confusion comes from recipe writers who claim it can be done in 30 minutes, but that’s simply not the case. Sure, you can brown onions in that time, but true caramelization—where sugar molecules break down into smaller, more flavorful compounds—requires at least 40 minutes for one onion.
Personally, I prefer caramelizing onions over low heat in a pan. There are tricks to speed it up, such as adding extra sugar or baking soda, but my laziness always wins out, so I let the onions' natural sugars develop at their own pace.
A sauté pan can only fit so many onions at once. If I’m making a large batch of jammy, sweet onions—or simply run out of stovetop space—I’ll turn to the oven. It takes longer, but it’s a more hands-off method and doesn’t require constant attention.
You have to keep them moist
When I first started caramelizing onions this way, I came across many recipes that recommended adding just a “splash” of water to prevent the onions from burning. That wasn’t enough. I begin by adding a full cup of water to the pan and continue to add more water as the onions cook. This ensures the environment remains moist, preventing the onions from browning too soon, and is especially crucial if you’re using your oven’s convection setting.
Apart from onions and water, you’ll only need a pinch of salt and a drizzle of olive oil. After that, it’s a waiting game—stir every 15 minutes or so, until the onions transform into a deeply colored, soft, and tender mass, ideal for adding to a dip, soup, or anything that could use a dollop of sweet, caramelized onions.
Keep them close together
When roasting vegetables, it's important to spread them out so they don’t become soggy and can brown and crisp around the edges. However, that’s not what we want here. Instead of spreading the onions, we’ll keep them clustered together. This helps them stay moist as they caramelize and ensures the pieces on the edges don’t cook faster than those in the middle. A silicone mat also prevents the onions from touching the pan, as the heat from the metal can cause them to brown too quickly and fry rather than caramelize.
Along with adding water every 15 minutes (or whenever it evaporates), you should stir as often. To do this, scoop the onions off the sheet pan and flip them towards the center, turning the outer layers inside and the top layers to the bottom. As the onions darken, increase your stirring frequency to every 10 minutes, and then every five, until they reach the perfect level of caramelization.
Caramelized Onions from the Oven
Ingredients Needed:
2 large onions, cut in half and sliced thinly
2 tablespoons olive oil
2 teaspoons salt
Water
Preheat your oven to 375°F and line a sheet pan with a silicone mat or parchment paper. Place the onions on the pan, tossing them with olive oil and salt using your hands.
Once the onions are in the center of the pan, pour in 1 cup of water and position the pan on the middle rack of the oven. Bake for 15 minutes, then stir the onions by flipping them so the outsides move to the inside and the top to the bottom. Repeat this every 15 minutes until they begin to darken and caramelize.
You might see a few charred or slightly burnt bits here and there, and that’s perfectly fine. If you notice this happening often, consider stirring more often, adding a bit more water, and pressing down the onions after stirring to prevent any bits from sticking out.
When the onions turn a golden brown, start stirring every 5-10 minutes until you achieve the desired level of caramelization. For two large onions, this process can take a couple of hours. They’re perfect for mixing into dips, spreading in grilled cheese sandwiches, or adding to soups and casseroles. Alternatively, you can simply eat them with a fork — they’re irresistible. The onions will stay fresh in the fridge for up to a week.
Updated at 1:56 p.m. EDT to include details about using silicone baking mats and a note on storage.
